Slope feature detection system

Abstract

A character feature detection system is provided for reliably reading non-touching hand printed and multi-font machine printed alphanumeric characters. An information field is scanned by a sensor array, and the sensor responses are digitized to form a binary character image. The image is thinned in one-cell layers as the image boundary and loops internal to the image are traced from boundary point to boundary point. A transition from one boundary point to another is defined by one of eight equally divergent vectors which are indicative of the local slope of a boundary between connected points. The sequence of vectors and their x-ray locations are recorded, and boundary slopes are indicated by a running average of four vectors representative of cell to cell transitions. Character features are detected from the sequence of boundary slopes to form a feature set including circumference counts, maximum and minimum image boundary limits, inflection points and loops. The image boundary is thinned to a one-cell stroke width, and character stops and nodes are located. Each stop arm is traced to identify valid stops, and the slope of each valid stop is determined to complete the feature set. The feature set is formatted and stored in a memory unit for character identification.